Biceps stretch is performed to increase the flexibility of the biceps brachii muscle.Relevant AnatomyThe biceps brachii muscle, familiarly known as the biceps, moves the arm forward and assists in turning the hand outward, a movement called supination. The biceps is a long muscle extending the length of the humerus. It arises in two places. It arises in two places; medially, the short head arises from the coracoid process of the scapula and laterally, the long head arises as a slender tendon from the supra glenoid tubercle inside the capsule of the shoulder joint. The tendon passes over the head of the humerus into a groove called the inter-tubercular sulcus. At this point the muscle has two bellies which fuse and then form a single tendon at the bottom. The tendon inserts on the tuberosity of the radius.The biceps brachii is active during unresisted elbow flexion with the forearm supinated and when the forearm is midway between supination and pronation in both concentric and eccentric contractions, but it tends not to be active when the forearm is pronated. However, when the magnitude of the resistance increases much beyond limb weight, the biceps is active in all positions of the forearm.read full article at [link]